Electric heater with add-on leads

ABSTRACT

An electric heater comprising a heater body including a sheath, a heating element within the sheath and at least one terminal extending from one end of the sheath. The heater further comprises an add-on (e.g., a flexible or a solid wire lead) lead secured to the terminal exteriorly of the heater body, an insulator surrounding the junction of the add-on and its terminal, and an oversleeve surrounding the insulator and overlying a portion of the sheath. The oversleeve is secured to the sheath thereby positively to hold the insulator in position relative to the heater body.

United States Patent [191 Portm'ann 3,839,623 Oct. 1, 1974 Temple Mn m"m m "n mmm Bn fl -nu hers WCLD 55772 66667 99999 HHHHH 2 96 6 200 324 09,393 75 08 62046 ,233 33333 1 ELECTRIC HEATER WITH ADD-ON LEADSInventor: Albert Lee Portmann, Labadie, Mo.

[22] Filed:

Primary Examiner- Volodymyr V. Mayewsky Attorney, Agent, or Firml(oenig,Senniger, Powers and Leavitt 21 App]. No: 393,039

[57] ABSTRACT An electric heater comprising a heater bod y including asheath, a heating element within the sheath and at least one terminalextending from one end of the sheath. The heater further comprises anadd-on (e.g., a flexible or a solid wire lead) lead secured to theterminal exteriorly of the heater body, an insulator surrounding thejunction of the add-on and its terminal, and an oversleeve surroundingthe insulator and overlying a portion of the sheath. The oversleeve issecured t0 the sheath thereby positively to hold the insulator inposition relative to the heater body.

3 Claims, 3 Drawing Figures 2 00 vAvA343 4 4 777 %MM ua 8 8800 355333 4399333 0 4 2 .n H 77 n. n 82 s S n n 053 T u.. u" N u "n 39 u n l E nu 2T u u 5 2 d m m" 0 4 A H H m .n P m mm m U MI w mm m mm m WW4 e 6 m a en e fl m ng ""4 rT 0 0 0 MwS DBSBVB "h 9 C D M E899334 2 T555666 S l99999 0 NHHH/// L03 435322 dfi lfl m n-l3 27348 F 52448 1 ,5 1 ll 1 68032 l6 3788 2 55 5 ll. .l 222333 BACKGROUND OF THE INVENTION This inventionrelates to electric resistance heaters and more particularly tocartridge heaters.

This invention is directly concerned with cartridge and tubular heatersto which electric power leads (e.g., flexible braided leads or specialsolid wire leads) may be added. Typically, cartridge heaters, such asthose described in the coassigned Desloge US. Pat. No. 2,831,951, have aresistance heating wire wrapped about a ceramic core to form a heatingcoil. The ends of this coil are connected to solid wire electrical powerleads (e.g., solid nickel alloy terminal pins) inserted intolongitudinal bores in the core so as to supply electrical power to thecoil. The core and the terminal wires are inserted in a metallic sheathwith the terminal pins extending outwardly from the sheath at one endthereof. A thermally conductive, electrically insulating material isplaced in the sheath to separate the coil from the sheath. The sheath isthen swage-formed so as to seal the core within the sheath and tocompact the electrical insulation thereby to provide increased heattransfer from the coil to the sheath. Tubular heaters are similar tocartridge heaters except that the heating coil is not wrapped about acore and that only one terminal wire extends from each end of theheater.

In many applications, the heater power leads are not required to bemoved or flexed once the heater is installed in a working position and,thus, solid wire terminals are well suited for power leads. However, inmany other instances the power leads are required to repeatedly flex, ora power lead of a different alloy is required. While solid wireterminals are preferred in many applications due to their good currentcarrying capacity, solid wire leads have the disadvantage of failing(breaking) under repeated flexing or bending. F lexible lead wires havebeen provided for cartridge heaters by crimping or otherwise securingflexible leads to the solid wire terminals extending endwise from oneend of the sheath. However, flexing of the flexible leads may placeundue strain on the junction between the solid terminal and the flexiblewires. An example of the above-described flexible lead connection isshown in US. Pat. No. 3,61 1,559. Also, in many known prior art heaterswith specially added leads, the junction of the special lead and theterminal pin is exposed to ambient conditions which may in turn causecorrosion of the junction. So-called compacted-in-place flexible leadshave been used with some success in cartridge heaters. Thesecompacted-in-place heaters utilize a stranded nickel or other hightemperature flexible wire inserted into the bores in the core to takethe place of the solid terminal wires. These flexible leads extend fromthe end of the heater and are compacted in place relative to the sheathin much the same manner as conventional solid leads. However, sincethese flexible leads are within the heated length of the heater, theyare usually attached to the heater in the early stages of manufacture,and these flexible leads are carried along at all subsequentmanufacturing steps thus adding to the complexity and cost ofmanufacturing the heater. Also, these compacted-in-place, stranded wireflexible leads do not have as long a service life as solid wire leads,and cannot be added to existing heaters.

SUMMARY OF THE INVENTlON Among the several objects of this invention maybe noted the provision of an electric heater having power leads added toa previously manufactured heater body in which the junction of the addedleads and the heater terminals are protected against strain; theprovision of such a heater in which leads of various materials (e.g.,flexible stranded wire or special alloy solid wire) may readily besecured to standard heater bodies; the provision of such a heater inwhich the added leads are protected from the relatively hightemperatures within the heater body; the provision of such a heater inwhich the unheated length of the heater is not substantially greaterthan similar heaters without added leads and in which the unheatedlength is constant regardless of the length of the heated length of theheater; the provision of such a heater with flexible leads having a wattdensity and long service life similar to heaters having solid wire powerleads; the provision of such a heater which is of rugged and economicalconstruction. Other objects and features will be in part apparent and inpart pointed out hereinafter.

Briefly, an electric heater of this invention comprises a heater bodyhaving a sheath, a heating element within the sheath, and at least oneterminal extending from one end of the sheath for supplying electricalpower to the heating element. The heater further comprises an add-onlead secured to the terminal exteriorly of the heater body, insulatingmeans surrounding the junction of the terminal and the add-on leads, andan oversleeve surrounding the insulating means and overlying a portionof the sheath. The oversleeve is secured to the sheath therebypositively to hold the insulating means in position relative to theheater body so as to relieve strain from the add-on leads at thejunction between the terminals and the add-on leads.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is an exploded perspective viewillustrating a cartridge heater of this invention having flexible leads,with some of the parts shown in section;

FIG. 2 is an enlarged longitudinal section of the heater showing thevarious parts in assembled relation prior to an oversleeve being securedin place to the heater; and

FIG. 3 is a view similar to FIG. 2, illustrating the heater aftersecuring of the oversleeve to the sheath.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODlMENT Referring now to the drawings,an electric cartridge heater of this invention, indicated in itsentirety at T, is shown to include a heater body 3 having a sheath 5, aheating element 7 disposed within the sheath, and a pair of terminalpins 9a,9b extending beyond one end of the heating element.

More particularly, the heater body 3 is similar to the cartridge heaterdisclosed in the coasigned Desloge US. Pat. No. 2,831,951 in which thesheath is a tube of stainless steel or other high-temperature metalclosed at one end. The heating element "7 includes a core 10 of ceramicmaterial or the like having two sideby-side bores lla,llllb extendinglengthwise therethrough. A length of resistance wire 13 is wrapped inhelical fashion about the outer cylindric surface of the core to form aheating coil. The end of the wire at each end of the coil is insertedinto a respective bore 11a or 11b (one wire end in each bore) in core10. A solid nickel alloy or other high-temperature conductor wireterminal pin 9a or 9b is inserted into a respective bore so that oneterminal pin is in electrical contact with one end of wire 13 and theother pin is in electrical contact with the other end of wire 13,thereby to connect the coil in series to the terminal pins and to thuscomplete a heating circuit. An electrical insulating powder 15 havingrelatively good thermal conductance, such as magnesium oxide (MgO),fills the gap within the sheath between the core and the inside of thesheath to electrically insulate the coil wire from the sheath and toenhance heat transfer from the heating element to the sheath. A lava orceramic end plug 17 having holes 19a,19b there'through for passage ofterminal pins 9a,9b, respectively, closes off the open end of thesheath. The entire sheath with the above-described parts and insulatingmaterial therein is then swage- 'formed to compress end plug 17 so as toclose the sheath, to compact insulating material 15, and to compresscore 10 so that terminal pins 9a,9b securely contact their respectiveends of coil wire 13. In FIGS. 2 and 3, heater body 3 is shown as apreassembled unit having been previously manufactured in accordance withthe above-described procedure. It will be noted that terminal pins 9a,9bextend beyond the end of the heater element a short distance (e.g., 5/16inch). The solid wire terminal pins provide high current carryingcapability and have minimal surface area so as to minimize oxidation ofthe portions of the terminal pins which are located within the heatedlength of the heating element and which are subjected to hightemperatures (e.g., 1,700F.).

In accordance with this invention, an add-on power lead 21a or 21b issecured at a respective junction 23a,23b to a respective terminal pin9a,9b. As shown, add-on leads 2la,21b are shown to be flexible leadshaving a plurality of small-diameter wires stranded or twisted togetherto form a flexible conductor 25; however, it will be understood thatother add-on leads, such as special alloy solid leads (not shown), maybe secured to terminal pins 9a,9b. A flexible insulation cover 27surrounds and insulates flexible conductor 25. As shown in FIGS. 2 and3, a short length of the conductor extends beyond the insulation coverat one end of the lead for securement to a respective terminal pin atjunctions 23a,23b. The flexible conductors are shown to be crimped toits respective terminal pin 9a,9b at junctions 23a,23b, but it will beunderstood that the flexible conductors may be secured to their terminalpins in any suitable manner, such as by welding or by soldering, as wellas by crimping. Preferably, insulation cover 27 is of braided fiberglass material or other material able to withstand relatively hightemperatures (e.g., 600 to 800F. or higher) and yet permit flexing ofthe leads. It will be understood, however, that other insulatingmaterial may be used, depending on the application for the heater.

A ceramic header or insulator 29 having a pair of longitudinal bores31a,3lb extending therethrough is applied to flexible leads 2la,2lb withbore 31a receiving lead 21a and with bore 31b receiving lead 211). Eachbore 3la,31b has an enlarged portion 33a,33b, respectively, forreception of a respective junction 23a,23b, with the remainder of thesebores being substantially the same cross section (i.e., diameter) as thecross section of leads 21a,2lb with insulation covers 27 thereon. Oneend of insulator 29, constituting its inner end, is adapted to bearagainst an adjacent end of heater body 3 with junctions 23a, 231)received in the enlarged portions 3311,3312 of bores 3la,31b and withthe flexible leads extending endwise from the insulator. Preferably,insulator 29 is molded of a ceramic material, such as steatite. With thediameter of bores 31a,31b substantially the same as the diameter as theflexible leads 2la,21 b, and with insulator 29 secured in place adjacentthe outer end of heater body 3, the insulator supports the flexibleleads and prevents strain from being placed on junctions 23a,23b due toflexing of the leads.

A cylindric oversleeve 35 having an inside diameter slightly larger thanthe outside diameter of sheath 5 is also applied to flexible leads2111,2112, this oversleeve being open at both ends. Its one end,constituting its outer end, is of decreased cross sectional area (i.e.,of decreased diameter) and is adapted to contact the outer surface ofinsulator 29 when the insulator is in abutting relation with the outerend of heater body 3. As shown in FIGS. 2 and 3, an inwardly projectingflange 37 is provided at the outer end of oversleeve 35 for engagementwith the outer end of insulator 29. Over sleeve 35 is longer thaninsulator 29 so that, with the insulator abutting against the heaterbody 3 and with flange 37 in engagement with the outer end of theinsulator, a portion of the oversleeve overlies the outer end portion ofsheath 5. Oversleeve 35 is a cylindrical member formed from thin-wall,stainless steel or other high-temperature tubing.

With the heater of this invention assembled as shown in FIG. 3,oversleeve 35 is secured to the outer end of sheath 5, as byroll-forming, swaging or by other diameter reduction processes. With theoversleeve secured to sheath 5, the outer diameter of the sheath and theouter diameter of the oversleeve are substantially the same and thetransition between the sheath and the oversleeve is substantially flush.It will be understood that with flexible leads 2311,23b secured toterminals 9a,9b as heretofore described and with the flexible leads21a,21b supported within bores 31a,3lb of insulator 29, and with theinsulator secured to the outer end of the sheath 5 by oversleeve 35, theflexible leads may be repeatedly flexed relative to the heater withoutdamage to the flexible leads or without damage to terminal pins 9a,9b.

It will be understood that the add-on leads of this invention may beused in conjuction with heaters other than cartridge heaters, such astubular heaters having one terminal extending from each end of theheater or other heaters having more than two terminals at each end ofthe heater.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. An electric heater comprising a metallic sheath of circular crosssection, a heating element within the sheath, means closing one end ofthe sheath, and at least one terminal extending from said one end of thesheath for supplying electrical power to the heating element, saidheater further comprising an add-on lead secured to said terminalexteriorly of said sheath, insulating means surrounding the junction ofsaid terminal and said add-on lead, said insulating means comprising arigid insulator having a longitudinal bore extending therethrough fromone end thereof to the other, said bore accommodating said add-on lead,and a metallic oversleeve of generally circular cross sectionsurrounding the insulating means and overlying a portion of said sheathadjacent said one end thereof, said insulator being adapted to abutagainst said one end of said sheath and against said closing means, saidoversleeve being open at its outer end for the passage therethrough ofsaid flexible lead, said outer end being of decreased cross-sectionthereby to engage said insulator and to hold it in abutting relationrelative to said one end of said sheath so as to relieve strain fromsaid junction, said oversleeve overlapping a portion of the sheath beingsecured to said sheath by means of a diam eter reduction processwhereupon after securing, the diameter of said sheath clear of saidoversleeve and the diameter of said oversleeve are substantially thesame so as to permit insertion of the heater in holes having a close fitwith said sheath.

2. An electric heater as set forth in claim 1 wherein said add-on leadis a flexible lead having flexible insulation on its exterior, saidinsulated flexible lead being adapted for reception in said bores insaid insulator.

3. An electric heater as set forth in claim ll further comprising a pairof terminals extending from said one end of the sheath and a pair ofadd-on leads, one for each terminal, wherein said insulating meanscomprises an insulator having two longitudinal bores extendingtherethrough, each said bore accommodating a respective add-on lead anda respective junction.

* l =l l=

1. An electric heater comprising a metallic sheath of circular crosssection, a heating element within the sheath, means closing one end ofthe sheath, and at least one terminal extending from said one end of thesheath for supplying electrical power to the heating element, saidheater further comprising an add-on lead secured to said terminalexteriorly of said sheath, insulating means surrounding the junction ofsaid terminal and said add-on lead, said insulating means comprising arigid insulator having a loNgitudinal bore extending therethrough fromone end thereof to the other, said bore accommodating said add-on lead,and a metallic oversleeve of generally circular cross sectionsurrounding the insulating means and overlying a portion of said sheathadjacent said one end thereof, said insulator being adapted to abutagainst said one end of said sheath and against said closing means, saidoversleeve being open at its outer end for the passage therethrough ofsaid flexible lead, said outer end being of decreased cross-sectionthereby to engage said insulator and to hold it in abutting relationrelative to said one end of said sheath so as to relieve strain fromsaid junction, said oversleeve overlapping a portion of the sheath beingsecured to said sheath by means of a diameter reduction processwhereupon after securing, the diameter of said sheath clear of saidoversleeve and the diameter of said oversleeve are substantially thesame so as to permit insertion of the heater in holes having a close fitwith said sheath.
 2. An electric heater as set forth in claim 1 whereinsaid add-on lead is a flexible lead having flexible insulation on itsexterior, said insulated flexible lead being adapted for reception insaid bores in said insulator.
 3. An electric heater as set forth inclaim 1 further comprising a pair of terminals extending from said oneend of the sheath and a pair of add-on leads, one for each terminal,wherein said insulating means comprises an insulator having twolongitudinal bores extending therethrough, each said bore accommodatinga respective add-on lead and a respective junction.